ZnO nanorods have been hydrothermally grown on substrates pre-coated with ZnO nanoparticles. This work presents the detailed chemistry to control the growth morphology and defects incorporation during the hydrothermal synthesis based on fine tuning the interfacial energy, the zinc solubility c. and surface charges. When c(o) < 0.88 mmol/l, a uniform coverage of nanorods is obtained and when c(o) > 1.56 mmol/l, large clustered rods are obtained. Finally, when 0.88 < c(o) < 1.56 mmol/l, a transition region where both nanorods and large clustered rods exist. We demonstrate that the type of native defects in the rods can be controlled by the pH of the growth conditions. In the region where the pH of the growth medium << point of zero charge (PZC), the major defects are hydrogen defects and zinc vacancies. In this regime, high-quality ZnO nanords with minimal visible emissions from deep level defects and strong UV band edge emissions can be grown. When pH >> ZC, the major defects are interstitial oxygen, interstitial zinc and zinc vacancies. In this regime, the intensity of the defect emissions is stronger than the UV emission. (C) 2009 Elsevier B.V. All rights reserved.